The present invention relates in general to fan assemblies that provide forced-air cooling in computer systems, and in particular to a fault-tolerant control and monitoring system for such fan assembly.
Most electronic equipment generate heat under normal operating conditions. Cooling systems are provided in those electronic systems where the generated heat may cause damage to the system components. Large computer systems and disc drive circuits are examples of equipment wherein provisions are made for forced-air cooling. A computer system typically includes one or more fan assemblies that provide for ventilation and cooling. Today's computer systems use fans with variable speed to reduce acoustic noise and increase power efficiency. The speed and functionality of the fan units must be monitored and controlled at all times to avoid damage to system components caused by high temperatures.
A common problem associated with fan control systems arises from any failure in the supply of power to the fan unit. Fan control systems must be designed to reduce the probability of such power failure and to detect it as soon as it occurs. Another drawback of some existing fan control systems is their inability to measure the exact speed of the fans. In these systems, a signal generated by a Hall-effect device inside the fan is first frequency-to-voltage converted, and then compared to two or more threshold voltages. Such systems are, therefore, capable of measuring the speed of each fan only within a range defined by the threshold voltages. Another associated drawback is the degree of control over the fan speed. Some existing fan control systems are capable of adjusting the fan speed at only two or three settings. In such systems, a dual fan assembly is commonly utilized such that when the speed of one of the fans drops below a certain threshold, the speed of the other fan is increased to compensate for the first fan.
Other functions that must be performed by fan control systems is physical presence detection. That is, the system must be capable of signaling the physical presence or absence of a fan unit. Finally, the control system itself must provide for fault detection mechanisms.
Thus, there exists a need for an improved fault-tolerant fan control and monitoring systems for use in electronic equipment.